GPS application using network assistance

ABSTRACT

A Global Positioning System (GPS) system comprises a user end, a mobile terminal, a positioning server, a GPS application server, and a base station network. The mobile terminal has a GPS receiver to receive GPS information from a plurality of GPS satellites. The positioning server is coupled to the user end through the network. The GPS application server is coupled to the network for communicating with the positioning server, and has a GPS receiver to receive GPS information from GPS satellites so as to calculate a position of the GPS application server. The geographic position of the GPS application server is known, and GPS assistant information is determined based on the calculated position and the geographic position of the GPS application server. The base station network communicates with the mobile terminal to obtain the GPS information of the mobile terminal and locate the mobile terminal based on the GPS information of the mobile terminal and the GPS assistant information.

CROSS REFERENCE TO PROVISIONAL APPLICATION

This application claims priority to the co-pending provisional patentapplication, Ser. No. 60/714,890, Attorney Docket Number O2-IP-0255P,entitled “GPS Application Using Network Assistance,” with filing dateSep. 6, 2005, and assigned to the assignee of the present invention,which is herein incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention is related to a Global Positioning System (GPS),and more particularly, to a GPS system for precisely locating theposition under an indoor environment.

BACKGROUND ART

The use of a Global Positioning System (GPS) satellite constellation forobtaining a terrestrial position fix (latitude, longitude, and altitude)is widespread and well known. It has been proposed that mobile terminals(such as, but not limited to, cellular telephones, personal digitalassistants, etc.) in modern wireless telecommunications systems includea capability to receive GPS signals and calculate position on thesurface of the Earth.

Under an indoor environment, GPS signals from the GPS satellites areweak. For implementing precise positioning indoors, GPS enabled devicesrequire not only a higher lever of sensitivity but also assistantinformation, such as Time Doppler shift, Broadcasting Ephemeris, andAlmanac for quick positioning. The assistant information is transmittedas Assisted GPS (AGPS) information. However, mobile networks do notsupport AGPS now in some areas.

SUMMARY OF INVENTION

The present invention provides a method and an approach for implementingthe transmission of the GPS assistant information so as to preciselylocate the position of a GPS device in a mobile phone under an indoorenvironment. Furthermore, the method or approach, in accordance withembodiments of the present invention, is also suitable to be operatedunder non-indoor situations.

The present invention implements a child locator system, in accordancewith one embodiment. In other embodiment, the present inventionimplements a locating service between any two terminals.

In accordance with one embodiment of the present invention, a GlobalPositioning System (GPS) system comprises a user end, a mobile terminal,a positioning server, a GPS application server, and a base stationnetwork. The mobile terminal has a GPS receiver to receive GPSinformation from a plurality of GPS satellites. The positioning serveris coupled to one user end through the network. The GPS applicationserver is coupled to the network for communicating with the positioningserver, and has a GPS receiver to receive GPS information from the GPSsatellites so as to calculate a position of the GPS application server.The geographic position of the GPS application server is known, and GPSassistant information is determined based on the calculated position andthe geographic position of the GPS application server. The base stationnetwork communicates with the mobile terminal to obtain the GPSinformation of the mobile terminal and locate the mobile terminal basedon the GPS information of the mobile terminal and the GPS assistantinformation.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments of the claimed subject matterwill become apparent as the following Detailed Description proceeds, andupon reference to the Drawings, wherein like numerals depict like parts,and in which:

FIG. 1 is a block diagram of a system for positioning the childterminal, in accordance with an embodiment of the present invention.

FIG. 2 is a block diagram of a system shown in FIG. 1 for showing theflow of information between a user end and a mobile terminal, inaccordance with one embodiment of the present invention.

FIG. 3 is a flow diagram showing a method for positioning a GPS mobileterminal, in accordance with an embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENT

Reference will now be made in detail to the embodiments of the presentinvention, GPS application using network assistance. While the inventionwill be described in conjunction with the embodiments, it will beunderstood that they are not intended to limit the invention to theseembodiments. On the contrary, the invention is intended to coveralternatives, modifications and equivalents, which may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

Furthermore, in the following detailed description of the presentinvention, numerous specific details are set forth in order to provide athorough understanding of the present invention. However, it will berecognized by one of ordinary skill in the art that the presentinvention may be practiced without these specific details. In otherinstances, well known methods, procedures, components, and circuits havenot been described in detail as not to unnecessarily obscure aspects ofthe present invention.

Referring to FIG. 1, a system 100 for locating the positions of mobileterminals 110A through 110N in accordance with one embodiment of thepresent invention is illustrated. The system 100 comprises one or moreuser ends 102A through 102N. Any one of the user ends 102A-N cancommunicate with a service provider (SP) server, such as a positioningserver 106, via a network. In accordance with one embodiment of thepresent invention, the user end 102A communicates with the positioningserver 106 via Internet 120 through TCP/IP (Transmission ControlProtocol/Internet Protocol) protocols so as to implement the real-time,rapid data communication.

Each of the user ends 102A-N can be any terminal which is coupled toInternet 120. For example, the user ends 102A-N include but are notlimited to a personal computer, a laptop computer, a Personal DigitalAssistant (PDA), etc. It will be apparent to those skilled in the artthat one of the user ends 102A-N also can be a terminal which is coupledto Internet 120 through a local area network (LAN) or a wireless localarea network (WLAN), in other embodiments of the present invention.

The system 100 according to the embodiment of the present inventionfurther comprises one or more electronic devices or GPS mobile terminals110 through 110N. Each of the mobile terminals 110A-N is provided withGPS functionality and comprises a corresponding GPS receivers 142A-N.The GPS mobile terminal 110 can be any type of cellular phone. Forexample, in accordance with one embodiment of the present invention, theGPS mobile terminal 110A is a GSM cellular phone.

In accordance with one embodiment of the present invention, the GPSreceiver 142A of the GPS mobile terminal 110A is able to acquire the GPSsatellites information from a plurality of GPS satellites 112. Forexample, locking onto the signals from multiple orbiting GPS satellitesprovides the capability to accurately calculate a position of the GPSmobile terminal 110A. In addition, the movement of the GPS mobileterminal 110A can also be tracked using signals from the orbiting GPSsatellites 112.

As mentioned hereinabove, the system 100 according to the embodiment ofthe present invention is used for locating the position of the mobileterminals 110A-N. In one example operation, the user end 102A is used tomonitor the positions of the mobile terminal 110A. The user end 102A cansend a request to the mobile terminal 110A for obtaining the positionsof the mobile terminal 110A, and thus serves as a parent end of thesystem 100. The mobile terminal 110A, after receiving the request fromthe user end 102A, sends the position information of the mobile terminal110A to the user end 102A, and thus serves as a child end of the system100.

Furthermore, in accordance with one embodiment of the present invention,the mobile terminal 110A-N can be attached to or carried by any movingdevices. For example, the mobile terminal 110A can be carried by avehicle, a taxi, a box car, a ship, item of consumer goods, etc. Assuch, the user end 102A can monitor the position of the moving deviceassociated with the mobile terminal 110A for managing or tracking themoving device.

As mentioned hereinbefore, the mobile terminal 110A requires assistantinformation for positioning. The system 100 comprises GPS applicationservers 104 for providing the GPS assistant information to the mobileterminal 110.

In accordance with one embodiment of the present invention, thepositioning server 106 is used to communicate data between the user ends102A-N and the GPS application severs 104A-N. For example, thepositioning server 106 is used to communicate data between the user ends102A-N and the GPS application servers 104A-N through the Internet 120,in one embodiment. As such, the positioning server 106 is working as acommunication center. In accordance with another embodiment of thepresent invention, one of the user ends 110A-N is constructed to work asa position server.

The GPS application server 104A comprises a GPS receiver 144A to acquirethe GPS signals from the GPS satellites 112, in accordance with oneembodiment of the present invention. The GPS application server 104A isstationary in one embodiment. The geographical position of the GPSapplication server 104A is fixed or known. In other words, the positioninformation, such as the longitude, the latitude, and the altitude, ofthe GPS application server 104A is known and constant. When the positioninformation of the GPS application server 104A and the positioninformation of the GPS signals received by the GPS receiver 144A of theGPS application server 104A are compared, the GPS assistant information,such as the Doppler shift, the number of satellites, reference time,reference location, can be obtained for the nearby area. Morespecifically, the position information of the GPS application sever 104Athat is known and constant is compared with position information of theGPS application sever 104A determined from GPS information from the GPSsatellites 112, As such, GPS assistant data can then be determined andused to compensate for GPS errors for all of the mobile terminals 110A-Nin that area.

In operation, a user can use any one of the user ends 102A-N to send arequest to the positioning server 106 for monitoring the position of aspecific mobile terminal of the mobile terminals 110A-N. In oneembodiment, each of the mobile terminals 110A-N has an individualidentification number. As such, a request from one of the user ends102A-N includes an identification number which corresponds to a specificmobile terminal of the mobile terminals 110A-N.

It will be apparent to those skilled in the art that a mobile phonesystem, such as a GSM network, may comprise a plurality of base stationsubsystems (BSS) each including a plurality of base stations (BS) orbase transceiver stations (BTS), and a plurality of base stationcontrollers (BSC). The base subsystems may be coupled to a network andswitching subsystem (NSS) for the handoff of data communications fromone BSS to another.

The system 100 according to an embodiment of the present inventionfurther comprises a wireless base station network of transmitting andreceiving stations (base station network 124). As shown in FIG. 1, thebase station network 124 is shown supporting mobile terminal 110A-N. Thebase station network 124 and the mobile terminals 110A-N communicatewith each other, and comply with a GSM network specification.

More specifically, as mentioned above, the base station network 124 hasa plurality of base stations (not shown). When one of the mobileterminals 110A-N communicates with the base station network 124, onlythe nearest base station the base stations of the base station network124 is used to communicate with the mobile terminal, for example, themobile terminal 110A. The positions of each of the base stations of thebase station network 124 are known. Therefore, the rough estimativeposition of the mobile terminal 110A can be known according to theposition the base station that is nearest to and communicating with themobile terminal 110A. Moreover, each of the mobile terminals 110A-N willkeep contacting or communicating with the corresponding nearest basestation (not shown) of the base station network 124, if the mobileterminals 110A-N are turned on, in one embodiment.

In accordance with one embodiment of the present invention, as anexample, after the positioning server 106 of the system 100 receives arequest from the user end 102A through the Internet 120, the positioningserver 106 communicates with the base station network 124 to obtain therough position or the city of the specific mobile terminal 110Atargeted. Then, according to the city of the specific mobile terminal110A, the positioning server 106 communicates with or transmits a signalto one of the GPS application servers 104A-N, which is located in thecity or near to the specific base station or the specific mobileterminal 110A.

The selected GPS application server 104A sends the GPS assistantinformation and a positioning request to the GPS receiver 142A of thetargeted mobile terminal 110A through the base station network 124.According to an embodiment of the present invention, the GPS applicationservers 104A-N can be located anywhere in the world. As mentioned above,the supporting GPS application server 104A comprises the GPS receiver144A for receiving GPS signals from the GPS satellites 112. As such,since the position of the GPS receiver 144A is known, the GPSapplication server 104A is able to calculate and provide the GPSassistant data to compensate for GPS errors in the nearby area.

Furthermore, when the positioning server 106 obtains the rough positionor the city of the specific mobile terminal 110A from the base stationnetwork 124, the supporting GPS application server 104A which is locatedin the same city or near the specific mobile terminal 110A communicateswith and provides the GPS assistant data to the specific mobile terminal110A.

In accordance with one embodiment of the present invention, the specificmobile terminal 110A receives the position request and the GPS assistantinformation through the base station network 124. For example, thecommunications between the mobile terminal 110A and the base stationnetwork 124 comply with a GSM network specification. The GPS receiver142A of the specific mobile terminal 110A acquires the GPS informationfrom the GPS satellites 112. In one embodiment, the position informationof the specific mobile terminal 110A is calculated according to the GPSinformation from the GPS satellites. In another embodiment, the positioninformation of the specific mobile terminal 110A is calculated accordingto the GPS information from the GPS satellites and the GPS assistantinformation from the nearby and supporting GPS application server 104A.The calculated position information is communicated to the GPSapplication server 104A or the positioning server 106 through the basestation network 124.

In accordance with another embodiment of the present invention, thespecific mobile terminal 110A receives the position request. The GPSreceiver 142A of the specific mobile terminal 110A acquires the GPSinformation from the GPS satellites 112. The mobile terminal 110A sendsthe GPS satellite information to the supporting GPS application server104A. In this case, the GPS information received by the GPS receiver142A from the GPS satellites 112 is sent to the nearby and supportingGPS application server 104A through the base station network 124. Theposition of the specific mobile terminal 110A is calculated at thenearby GPS application server 104A. In addition, the GPS assistant datacan also be provided by means of the nearby and supporting GPSapplication server 104A for accurately calculating the position of thespecific mobile terminal 110A. Therefore, as to GPS mobile terminal110A, the power consumption and the dimensions of the GPS chip can besignificantly reduced.

In accordance with another embodiment of the present invention, thespecific mobile terminal 110A receives the position request. The GPSreceiver 142A of the specific mobile terminal 110A acquires the GPSinformation from the GPS satellites 112. The mobile terminal 110A sendsthe GPS satellite information to the positioning server 106. In thiscase, the GPS information received by the GPS receiver 142A from the GPSsatellites 112 is sent to the positioning server 106 through the basestation network 124. The position of the specific mobile terminal 110Ais calculated at the positioning server 106. In addition, the GPSassistant data can also be provided by means of the nearby andsupporting GPS application server 104A and sent to the positioningserver 106 for accurately calculating the position of the specificmobile terminal 110A. Therefore, as to GPS mobile terminal 110A, thepower consumption and the dimensions of the GPS chip can besignificantly reduced.

In one embodiment, the position data of the specific mobile terminal110A is sent to the positioning server 106 through the Internet 120. Thepositioning server 106 will further transmit the position data of thespecific mobile terminal 110A to the user end 102A through the Internet120. The position data is geographic information or data.

In accordance with another embodiment of the present invention, thesystem 100 according to an embodiment of the present invention furthercomprises an electrical map (e-map) server 108 to provide an e-map andshow the position of the specific mobile terminal in the form of thee-map. In another embodiment, the e-map server 108 is coupled to thepositioning server 106 and the user end 102A through the Internet 120.The user can read the e-map through a browsing tool or a browser of aserver provided by the positioning server 106. As such, the positioningserver 106 can provide GPS data related to the mobile terminal 110A tothe e-map server 108 via the Internet 120. The e-map server 108 is ableto integrate the GPS data, combining with GPS assistance data ifnecessary, into an e-map. The e-map server 108 sends to the user ends102A an e-map that also integrates the position of the mobile terminal110A.

The position of the mobile terminal 110A can be shown on the E-map. Theuser can monitor the position of the mobile terminal 110A at the userend 102A. As such, the user has visual information indicating thegeographic position of the mobile terminal 110A overlaid on an E-map, inone embodiment. Further, in accordance with one embodiment of thepresent invention, the e-map server 108, the positioning server 106 andthe GPS application server 104A as shown in FIG. 1 are provided by aservice provider.

Referring to FIG. 2, a flow of information between the user end 102A andthe mobile terminal 110A shown in FIG. 1 is illustrated. The user end102A and the mobile terminal 110A in FIGS. 1 and 2 are taken as adescriptive example for illustrating how to use the user end 102A forlocating the mobile terminal 110A.

As shown in FIG. 1, using the user end 102A to locate the mobileterminal 110A, a request with the identification number of the mobileterminal 110A is sent to the positioning server 106 through the Internet120. It will be apparent to those skilled in the art that the mobileterminal 110A keeps communicating with the nearby base station, if it isturned on. The positioning server 106 communicates with the base stationnetwork 124. As such, the nearby and supporting base station can beknown according to the identification number of the mobile terminal110A.

Once the nearby and supporting base station is known, the mobileterminal 110A can be located with a rough area or a city such that thenearby GPS application server 104A can be determined. Further, the GPSassistant data in the rough are determined by the nearby GPS applicationserver 104A. Another request then will be sent to the mobile terminal110A to activate the mobile terminal 110A for receiving GPS informationof the mobile terminal 110A from the GPS satellites 112. The positiondata of the mobile terminal 110A can be calculated or determined on thebasis of the GPS information from the GPS satellites 112 and the GPSassistant data from the GPS application server 104A. As mentioned above,the calculation of the position data of the mobile terminal 110A can beat the mobile terminal 110A, the GPS application server 104A, or thepositioning server 106. The positioning server 106 obtains the positiondata of the mobile terminal 110A and then sends it the user end 102A.The e-map can be sent to the positioning server 106 to virtually showthe position of the mobile terminal on the e-map.

Referring to FIG. 3, a method 300 for obtaining the position of anelectrical device, such as a GPS mobile terminal, in accordance with oneembodiment of the present invention is illustrated. At 302, a user canuse a user end, such as a computer or a personal digital assistant(PAD), to send a request to a positioning server through a communicationnetwork, such as the Internet, for locating any one of a plurality ofmobile terminals. The request includes an identification number tospecify a specific mobile terminal of the plurality of mobile terminals.

At 304, once the position server receives the request, the positioningserver communicates with a mobile communication network, such as awireless base station network or a base station network, to recognizethe rough position or the city of the specific mobile terminal. Inaccordance with one embodiment of the present invention, the mobilecommunication network complies with GSM standard, and the mobileterminals are mobile phones. It will be apparent to those skilled in theart that the mobile communication network comprises a plurality of basestation networks each having a plurality of base stations. Any one ofthe mobile phone communicates with a nearby base station, the positionor corresponding geographic information of which is known. As such, thespecific mobile terminal can be located within a city or a rough areawhich is near the supporting base station communicating with thespecific mobile terminal.

At 306, the positioning server transmits another request to a GPSapplication server in the city or the rough area, or a nearest GPSapplication server for acquiring GPS assistant data with the rough area.The supporting GPS application server comprises a GPS receiver forreceiving GPS information from a plurality of GPS satellites so as tocalculate a GPS position information of the GPS application server. Theposition of the GPS application server is known. Comparing thecalculated GPS position information and the position of the GPSapplication sever, GPS assistant data for the corresponding geographicarea can be determined to compensate for GPS errors for all of themobile terminals in that area.

At 308, a request is sent to the specific mobile terminal through thebase station network to activate the specific mobile terminal to receivethe GPS information from the GPS satellites. The mobile terminalaccording to an embodiment of the present invention comprises a GPSreceiver for receiving he GPS information from the GPS satellites.

At 310, position data of the specific mobile terminal is calculated onthe basis of the GPS information received by the mobile terminal fromthe GPS satellites and the GPS assistant data from the GPS applicationserver. In accordance with one embodiment of the present invention, theGPS assistant data is also transmitted to the specific mobile terminalthrough the base station network. In this case, the position informationof the specific mobile terminal can be calculated at the specific mobileterminal, and transmitted to the GPS application server.

Alternatively, in accordance with one embodiment of the presentinvention, the GPS assistant data is not transmitted to the mobileterminal, and the position information of the specific mobile terminalis calculated at the GPS application server. In this case, the GPSinformation received by the mobile terminal from the GPS satellites istransmitted to the GPS application server, and, together with the GPSassistant data, is used to calculate the position information of thespecific mobile terminal.

At 312, the calculated position data of the specific mobile terminal istransmitted to the positioning server through the base station network.

At 314, an e-map provider server provides an e-map, which is transmittedto the positioning server through the Internet. In accordance with oneembodiment of the present invention, the e-map server is able tointegrate the GPS data, combining with GPS assistance data if necessary,into an e-map. The e-map server sends to the user end an e-map that alsointegrates the positions of the one or more targeted mobile terminals.

At 316, the position data of the specifically targeted mobile terminalis shown on the user end. The position of the mobile terminal can beshown on the E-map. The user monitors the position of the mobileterminal at the user end. As such, the user has visual informationindicating the geographic position of the mobile terminal overlaid on anE-map.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be understood that variousadditions, modifications and substitutions may be made therein withoutdeparting from the spirit and scope of the principles of the presentinvention as defined in the accompanying claims. One skilled in the artwill appreciate that the invention may be used with many modificationsof form, structure, arrangement, proportions, materials, elements, andcomponents and otherwise, used in the practice of the invention, whichare particularly adapted to specific environments and operativerequirements without departing from the principles of the presentinvention. The presently disclosed embodiments are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the invention being indicated by the appended claims and theirlegal equivalents, and not limited to the foregoing description.

1. A method for locating, comprising: locating a general geographic area of an electronic device; calculating GPS assistant information according to said general geographic area; and sending said GPS assistant information to said electronic device through a mobile communication network.
 2. The method of claim 1, further comprising: receiving a request at a positioning server from a requesting device for locating said electronic device; and sending said request comprising said GPS assistant information from said positioning server to said electronic device through said mobile communication network.
 3. The method of claim 2, further comprising: receiving GPS satellite information at said electronic device from a plurality of GPS satellites; and calculating a geographic position of said electronic device using said GPS satellite information and said GPS assistant information; and sending said geographic position to said requesting device.
 4. The method of claim 3, wherein said calculating a geographic position comprises: sending said GPS satellite information and said GPS assistant information from said electronic device to said positioning server through said mobile communication network; and calculating said geographical position of said electronic device at said positioning server.
 5. The method of claim 3, wherein said calculating a geographic position comprises: calculating said geographical position using said GPS satellite information and said GPS assistant information at said electronic device.
 6. The method of claim 1, further comprising: tracking said electronic device using said geographical position.
 7. The method of claim 2, wherein said receiving a request further comprises: receiving said request through an internet network.
 8. The method of claim 1, wherein said calculating GPS assistant information comprises: receiving satellite information from a plurality of GPS satellites by a GPS application server, wherein a geographic position of said GPS application server is known; calculating a GPS position of said GPS application server based on said GPS satellite information; and comparing said GPS position and said geographic position to determine said GPS assistant information.
 9. The method of claim 1, wherein said locating a general geographic area comprises: establishing communication between said electronic device and a nearby base station of a base station network, wherein said electronic device is within a predetermined distance from said nearby base station; and associating said general geographic area with a location of said nearby base station.
 10. A method for locating a mobile terminal, comprising: receiving a request from a requesting device for locating a mobile terminal; locating a general area of said mobile terminal; calculating GPS assistant data according to said general area; sending said request comprising said GPS assistant information to said mobile terminal through a mobile communication network such that a geographical position of said mobile terminal can be determined; receiving position information of said mobile terminal that is based on said GPS assistant data and GPS satellite information associated with said mobile terminal through said mobile communication network; determining a geographical position of said mobile terminal; and sending said geographical position to said requesting device.
 11. The method of claim 10, wherein said receiving position information comprises: receiving said position information comprising said geographical position wherein said geographical position is calculated at said mobile terminal.
 12. The method of claim 10, wherein said determining a geographical position comprises: calculating said geographical position based on said GPS assistant data and said GPS satellite information.
 13. The method of claim 10, wherein said determining GPS assistant information further comprises: receiving GPS satellite information from said plurality of GPS satellites by a GPS application server, wherein a geographic position of said GPS application server is known; calculating a GPS position of said GPS application server based on said GPS satellite information; comparing said GPS position and said geographic position of said GPS application server so as to determine said GPS assistant information.
 14. The method of claim 10, wherein said locating a general area of said mobile terminal further comprises: establishing communication between said mobile terminal and a nearby base station of a base station network, wherein said mobile terminal is within a predetermined distance from said nearby base station; and associating said general geographic area with a location of said nearby base station.
 15. A GPS system, comprising: a user end; a mobile terminal having a GPS receiver to receive GPS information from a plurality of GPS satellites; a GPS application server coupled to said user end, said GPS application server comprising a GPS receiver to receive GPS information from said plurality of GPS satellites to determine a GPS position of said GPS application server, wherein a geographic position of said GPS application server is known, and GPS assistant information is determined based on said GPS position and said geographic position of said GPS application server; a base station network communicating with said mobile terminal to obtain said GPS information of said mobile terminal and locate said mobile terminal based on said GPS information received by said mobile terminal and said GPS assistant information.
 16. The GPS system of claim 15, further comprising an E-map server for providing an E-map so as to show a geographic position of said mobile terminal.
 17. The GPS system of claim 15, further comprising a network for communicating with said user end, said GPS application server, and said base station network.
 18. The GPS system of claim 15, wherein said mobile terminal has an identification number such that said user end specifies said mobile terminal through said identification number.
 19. The GPS system of claim 15, wherein said base station network comprises a plurality of base stations, and one base station of said plurality of base stations communicates with said mobile station.
 20. The GPS system of claim 15, wherein said user end comprises a mobile phone. 